1. Field of the Invention
This invention relates to a ceramic valve which in turn moves to open and close an intake and exhaust port of an engine cylinder, and particularly concerns to an improved structure to movably support a ceramic valve.
2. Description of the Prior Art
In recent years, high rotation with high power has been required for an internal combustion engine in use for an automobile. A valve, adapted to open and close an intake and exhaust port of an engine cylinder, is exposed to severe environment both mechanically and thermally. Light weight and heat-resistant ceramics is considered to apply to the valve so as to endure the severe environment.
In this instance, a valve (b) supports its stem (s) by a retainer (r) through a cotter (c) as seen in FIG. 14a. The outer surface of the cotter (c) and the inner surface of the retainer (r) are both tapered to tightly engage each other by the action of wedge.
In accompaniment with the valve action, the cotter (c) acts to engage with the stem (s) more tightly by the effect of wedge, the maximum intensity of which works at the lowest end (n) of the retainer (r). The retainer (r) makes its end (n) tightly act to the stem (s) through the lowest end (m) of the cotter (c), leading to stress concentration at the stem (s) so as to result in crack or breakage as seen at denotation (k) in FIG. 14a.
Another problem is shown by the prior structure, in which the cotter (c) provides a lock projection (p) semi-circular in section at the inner surface to interfit an annular groove (g) provided at the outer surface of the stem (s) as shown in FIG. 7c.
In association with the action of the valve (b), the projection (p) acts to tightly engage with the open ended portion of the groove (g), thus leading to establish stress concentration so as to end up in crack or breakage as seen at denotation (k) in FIG. 7c.
In addition, with the axial displacement of the valve (b), the cotter (c) comes to engage with the stem (s) more tightly under the influence of wedge effect. The lengthwise sharp edge (e) of each piece tightly engages with the outer surface of the stem (s) so as to cause stress concentration, resulting in crack or breakage as seen at denotation in FIG. 7d.
Therefore, it is an object of this invention to provide a ceramic valve supporting structure which is capable of preventing stress concentration from being developed upon a valve stem in a structure in which the ceramic valve is supported by way of a cotter.
It is another object of this invention to provide a ceramic valve supporting structure which is capable of obtaining a long servicing life with simple structure and minimum cost.
According to this invention, there is provided a ceramic valve supporting structure comprising a ceramic valve having an integral stem, the upper portion of which is provided with a circular groove in concentrical relationship with said stem, and arranged to axially displace so as to alternately open and close an intake and exhaust passageway communicating with a combustion chamber of an internal combustion engine, a cotter the outer surface of which is tapered, and formed by butting a pair of semi-cylindrical pieces, and having a lock member placed into said groove when secured concentrically to the outer surface of said stem, a cylindrical retainer concentrically secured to the outer surface of said cotter so as to support said valve through said cotter, said retainer being provided with the inner surface tapered in a direction so as to make said cotter tightly engage with the outer surface of said stem by means of wedge effect against said tapered cotter due to the urging force of a spring member axially exerted on said retainer, and a stress relief means provided so as to avoid the predetermined portion of said cotter from locally engaging against the outer surface of said stem.